Traditionally, higher performance sealants and caulks have been formulated using solvent based polymer systems such as silicone and polyurethane polymers as the binder for the sealant formulation. These solvent based types of sealant formulations generally yield sealants with good application properties (thixotropy and viscosity) and in the cured form typically have the elastomeric properties and adhesion required for a high performance sealant or caulking material. However, in recent years, with increasing government regulation and heightened consumer awareness, the manufacturers of solvent based sealants are coming under increasing pressure to reduce the VOC (volatile organic content) of their product (i.e. organic solvent content).
Dispersions of polymer particles in water have been used extensively in water-based sealants such as coatings and caulking. Their low viscosity, low volatile organic emissions, and ease of application have been favorable factors for their use. However, irrespective of the polymer particle sizes there has been a barrier at from 40-65% solids (depending on emulsifier type and other conditions) above which dispersions of polymer particles are difficult to prepare. Therefore high solids sealants were made by adding fillers. The fillers dilute the polymer in the final application lowering elongation and increasing modulus. Polymers having low Tg values (such as below 0.degree. C.) which are particularly useful in formulating sealants and caulks requiring low temperature flexibility are sticky.
One example of high solids polymerization is European Patent Publication No. 0 515 719 A1, which discloses a self-adhering acrylate copolymer, which can be used for the production of self-adhering surface layer formulations. This acrylate copolymer is produced by a combined suspension and emulsion polymerization. The solids content recited are 30-70 wt. % and the examples show 65 wt. % solids.
An article by Do Ik Lee in the Journal of Paint Technology, Vol. 42, No. 550 (1970) pp 579-587 discusses the packing of binary mixtures of spheres.
U.S. Pat. No. 4,130,523 to Hoy and Peterson discloses nearly 70 volume % solids. Their latex particles are desirably no larger than 1.5 microns in diameter.
It is the object of the current application to polymerize in the presence of a preformed latex additional monomers creating a high solids, low viscosity, thixotropic product especially useful in coatings and sealants.